Rubber compositions typically contain particulate filler reinforcement to promote enhancement of physical properties of the rubber composition.
Conventional filler reinforcement used for rubber compositions is typically at least one of rubber reinforcing carbon black and silica such as, for example, precipitated silica, including combinations of rubber reinforcing carbon black and the silica.
Tires conventionally have at least one component comprised of such filler reinforced rubber composition.
For this invention, a reinforcing filler combination is proposed which is comprised of what is believed to be a synergistically effective combination of rubber reinforcing carbon black, optionally precipitated silica and granular functionalized mineral (coupling agent pretreated mineral), where said mineral is comprised of at least one of aluminum hydrate (AlOOH) and titanium dioxide (TiO2), preferably aluminum hydrate, as rubber reinforcing fillers to promote a beneficial viscoelastic response for the rubber composition.
Such pretreated minerals are provided in a granular form in contrast to a rod configured form. Such pretreated nanoparticle granular minerals are provided exclusive of composites of such minerals and silica.
It is envisioned that such combination of reinforcing fillers can provide a viscoelastic response for a rubber composition which contains conjungated diene-based elastomer(s) which differs from using reinforcing fillers limited to a combination of rubber reinforcing carbon black and precipitated silica.
It is preferred that the granular pretreated mineral fillers are of a nanoparticle size having an average diameter in a range of from about 10 to about 500, alternately from about 10 to about 300 nanometers (nm).
The aluminum hydrate (AlOOH) is of unique interest for achieving a relatively high rubber reinforcement effect and special rubber/filler interactions to promote vehicular tire rolling resistance reductions and increased wet traction performance for a tire having a tread containing a pre-treated aluminum hydrate.
Coupling agents used for pre-treating the granular mineral fillers prior to their addition to the rubber composition have a moiety reactive with said granular AlOOH and TiO2 mineral fillers, particularly the granular AlOOH, and another different moiety interactive with diene-based elastomer(s) of said rubber composition.
Representative of such coupling agents include, for example, polysulfide based coupling agents which contain end functional groups which can chemically react with the AlOOH and TiO2 mineral fillers, particularly the granular AlOOH filler, such as, for example, carboxyl and siloxy groups, particularly carboxyl groups.
Historically, it has heretofore been suggested to use various aluminum oxides and hydroxides for rubber reinforcement which have been pretreated with a coupling agent where a rod form of aluminum hydrate (AlOOH) has been exemplified without exceptional results. For example, see U.S. Pat. No. 7,718,717.
However, for this invention, it has surprisingly been discovered that a granular from of aluminum hydrate (AlOOH) pretreated with a coupling agent provided an unexpectedly beneficial viscoelastic response in a sense of appearing to provide a synergistic result of combining the pretreated AlOOH with a combination of rubber reinforcing carbon black and precipitated silica to achieve an unexpectedly high rubber reinforcing effect together with a beneficially low hysteresis effect for the rubber composition and predictive improved wet performance for a tire with a tread of such rubber composition.
By the term viscoelastic response it is contemplated that viscoelastic behavior is to be effected by an inclusion of the aforesaid granular from of aluminum hydrate (AlOOH) in a sense of promoting beneficial physical properties for a rubber composition.
It was unexpectedly discovered that the combined inclusion of the pretreated, functionalized, granular aluminum hydrate (AlOOH), instead of the rod form of AlOOH, with a combination of rubber reinforcing carbon black and precipitated silica can be beneficially used to promote a reduction in rubber hysteresis as evidenced desirable tan delta measurements with predictive beneficial reduction in rolling resistance for an associated rubber tire having a tread of such rubber composition.
Data reported in the literature (Hiroshi Mouri, et al, Rubber Chemistry and Technology, 72 (1999), Pages 960 through 968) reported that aluminum trihydrate, namely Al(OH)3, exhibited different dynamic viscoelastic response to frequency sweep measurement for a plot of loss modulus (G″) versus a very high frequency at which was greater than the loss modulus (G″) for both silica and carbon black.
The very high frequency tan delta measurements for the rubber compositions are referred to as a result of a very high tan delta test frequency of 105 Hertz, at a temperature of about 23° C. and dynamic strain of about one (1) percent.
It is envisioned that such high frequency tan delta value is a predictive indication of the rubber composition's beneficial promotion of wet traction for a vehicular tire tread when containing the aluminum trihydrate
Such data referred to in that literature also reported low frequency tan delta values for the rubber compositions at a lower frequency of 10 Hertz at a temperature of about 23° C. and dynamic strain of about 1 percent.
It is envisioned that such low frequency tan delta test value is a predictive indication of the rubber composition's promotion of reduced hysteresis for the rubber composition when containing the aluminum trihydrate with predictive beneficial reduction in rolling resistance for a tire with tread of such rubber composition.
In the description of this invention, the term “phr” where used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
In the description of this invention, the terms “rubber” and “elastomer” where used herein, are to be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The terms vulcanize and cure where used therein are used interchangeably unless otherwise indicated.